Heavy oils, such as high-metal content crudes and resids, are under investigation as sources for valuable hydrocarbons. The upgrading of these oils can be accomplished via processes such as solvent extraction to remove metals and other impurities therefrom. Improvements in the subcritical or supercritical solvent extraction of such oils are increasing the viability of these carbonaceous materials as sources of hydrocarbons. These improvements are specifically aimed at upgrading heavy crude oils so that high yields of extract product can be refined by conventional catalytic technology such as resid hydrodesulfurization and catalytic cracking.